GPRS (General Packet Radio Service) is a standard and an extension to the GSM (Global System for Mobile Communications) standards to provide wireless packet data services on GSM cellular networks. In GPRS, user data is served to each mobile node (MN) by a Serving GPRS Support Node (SGSN) that provides a wireless GSM compatible connection. The SGSN is an ingress router for the mobile node and the first routing element visible to the mobile node. Each SGSN is contained within a Public Land Mobile Network (PLMN) that may contain many SGSN's, each communicating with many different mobile nodes.
User data to and from the mobile node is transported in the PLMN over an IP (Internet Protocol) backbone with data units being tunneled over the backbone using a tunneling protocol called GPRS Tunneling Protocol (GTP). GTP runs between the SGSN's, and a Gateway GPRS Support Node (GGSN) and is carried as User Datagram Payload (UDP) over IP. The GGSN is an anchor and egress router in GPRS through which all packets flow. GTP provides seamless mobility for the mobile nodes between and within each PLMN in a GPRS system. All packets in a GPRS network flow between a GGSN and a SGSN with at least one SGSN being associated with a mobile node at all times.
Mobile Internet Protocol (Mobile IP or MIP, including MIPv4 and MIPv6) is an Internet Engineering Task Force (IETF) network layer protocol. MIPv4 is defined in RFC 3220 (Request for Comments) of the IETF (Internet Engineering Task Force) of the IAB (Internet Architecture Board). The standards for MIPv6 is currently in draft form and is soon to become an RFC. It is designed to allow seamless connectivity and TCP (or other connection oriented transport protocol) session maintenance when a mobile node moves from one LP subnet to another. MIPv4 uses two network infrastructure entities, a Home Agent (HA) and an optional Foreign Agent (FA), to deliver packets to the mobile node when it has left its home network. MITPv4 also supports point-of-attachment Care-of Addresses (CoA) if a FA is unavailable. Mobile IP is increasingly being deployed for 2.5/3G (2.5 or third generation wireless) provider networks.
It has been proposed that a Mobile IP Foreign Agent be located at each GGSN in a GPRS network in order to support movement by mobile nodes between GPRS and Mobile IP networks (see e.g. Technical Specification of the Third Generation Partnership Project 3GPP TS 23.923). A mobile node moving into a GPRS service area would find the Foreign Agent and perform a Mobile IP registration through the Foreign Agent. Data traffic with the mobile node can then be tunneled between the GPRS Foreign Agent and a conventional Home Agent in the mobile node's home network. For each consumer that wants application-transparent constant connectivity and reachability with respect to the consumer's home network, a Home Agent must be deployed in the consumer's home network.
This proposal further requires changes to GPRS standards and adds significantly to overhead on the network. The FA must constantly advertise its presence to incoming mobile nodes on the network adding to network overhead. In addition, the FA and the HA in the home network must always be active adding to processing demands. Further, the packet routing must be altered resulting in security and routing overhead going outside the PLMN to the mobile node's HA. As a result, proxy or gratuitous Address Resolution Protocol (ARP) must be performed by the HA to maintain reachability and connectivity. Moreover, the original GPRS mobility management must be replaced by Mobile IP-based mobility management even when the mobile node is in the PLMN. Accordingly, this scheme cannot be deployed in stages, since all GGSN's, SGSN's and mobile nodes must be changed to support the new mobility mechanism.
Finally, the system only works if both a Home Agent and a Foreign Agent can be provided for the mobile node. The Home Agent, now a single point of failure, is located outside the GPRS network and may therefore be outside the control of the GPRS operator. Foreign Agents also are not supported in MIPv6, so compatibility problems may arise with networks operating on MIPv6.